Investigations from abroad suggest that idiopathic preterm delivery may be due to ascent of microorganisms from the cervix. These may then colonize the decidua, foetal membranes and amniotic fluid and may thus precipitate preterm contractions or rupture of the membranes. In subclinical urogenital infections, antibiotic treatment appears, in some cases, to be capable of reducing the risk of preterm birth. In cases of treated premature delivery, antibiotic treatment may possibly prolong the pregnancy and prevent neonatal and puerperal infections. Further investigations are, however, recommended before introduction of routine antibiotic treatment in cases of threatened premature birth.